where \(\beta _t \in (0, 1)_{t=1}^T\)  are set by a variance schedule. We use the cosine variance schedule [1]} with \(T=1000\)  timesteps:
\(\beta _t = \text{clip}\left(1 - \frac{\bar{\alpha }_t}{\bar{\alpha }_{t-1}}, 0.999 \right) \quad \bar{\alpha }_t = \frac{f(t)}{f(0)}\quad f(t) = \cos \left( \frac{t/T + s}{1 + s} \cdot \frac{\pi }{2} \right)\) 
